Whenever dealing with equations, it is necessary to let the textbook define the variables - as not all textbooks use the same definitions. All that said, in aerodynamics, it is normal to define the drag coefficient as the sum of the profile drag and the induced drag.
CD = Cd + k CL2
The left side of this equation applies to wings of fixed length. The first term on the RHS is the profile drag and it is usually defined as the drag coefficient associated with an "infinite wing" length - that is to say, what you obtain when measuring drag on a wing that spans the width of a wind-tunnel. The second term on the RHS is the induced drag, and results from the fact that a wing of finite length has more drag than a wing of infinite length. Therefore, if this is what your equation is referring to, then the CD0 term in your question is the profile drag, and you would obtain it by finding wind-tunnel tests for the wing you are considering. NACA was started to provide such things.

However, as profile drag itself follows the same basic curve as the total drag, it is also possible that your equation is being applied to a wing of infinite length. In that case, CD0 would simply be the drag coefficient when CL = 0. (ie the intercept of the curve with the CD axis).